Pressure actuated switch



y Patented Nov. 23, 1943 PRESSURE ACTUATED SWITCH Erle Martin, WestHartford, and Thomas E. Doherty, 'South Glastonbury, Conn., assignors toUnited Aircraft Corporation, East Hartford, Conn., a corporation ofDelaware Application December 27, 1940, serial No. 311,868

(ci. zoo-s2) 13 Claims.

This invention relates to improvements in hydraulic control devices andhas particular reference to an improved control unit for ahydrocontrollable feathering-type propeller.

An object of the invention resides in the cornbination of an improvedpressure actuated electric switch for discontinuing the application ofpressure to a hydraulic mechanism when the pressure has reached apredetermined value.

A further object resides in the\provision of ai# 10 improved pressureactuated switch of the character indicated which is responsive to adifference in the inlet and exhaust pressures of a hydraulic mechanismsuch as a propeller pitch changing mechanism.

A still further object resides inthe provlsionl-' of an improvedpressure actuated switch' of the character indicated which may beconnected into a hydraulic circuit without danger of leakage ofhydraulic fluid through or from the switch mechanism and in which theswitch contact points are immersed in hydraulic fluid which tends todamp any tendency of the electric current to arc at the contact points.

Other objects and advantages will be more particularly pointed outhereinafter or will become apparent as the description proceeds;

In the accompanying drawing in which like reference numerals are used todesignate similar parts throughout,.there is illustrated in two somewhatdifferent forms a suitable mechanical arrangement for the purpose ofdisclosing the invention. The drawing, however, is for the purpose ofillustration only and is not to be taken as limiting or restricting theinvention since it will be apparent to those skilled in the art thatvarious changes in the illustrated construction may be resorted towithout in any way exceeding the scope of the invention.

In the drawing,

Fig. 1 is a schematic partly sectional view of a hydro-controllablefeathering-type propeller.

Fig. 2 is a schematic view of the control apparatus for such a propellerschematically illustrating the manner in which a pressure actuatedswitch such as that constituting the invention is incorporated therein.f l

Fig. 3 is a detailed sectional view on an enlarged scale of a pressureactuated switch constructed according to the invention, the switch beingshown in operative position with respect to a member of the controlapparatus through whichfiuid conduits extend, and

tuated'switch constructed according to the invention.

Referring to the drawing in detail, the numeral I 0 generally indicatesa propeller driving shaft projecting from an engine generally indicatedat I2 and carrying a hydro-controllable featheringtype propellergenerally indicated at I4. This propeller may be of the typeparticularly illustrated and described in my co-pending United Statesapplication Serial No. 184,792, filed January 13, 1938, for Featheringpropeller control, and may have a hub I6 carrying a plurality of blades,one of which is indicated at I8, rotatably mounted therein for pitchchanging movements.

Each blade may be provided with a gear member 2|) all of which mesh witha gear 22 carried by a V rotatable cam member 24 which is in turnsupported in a fixed cam member 26 for changing the pitch of thepropeller blades. The cam 24 may be rotated by means of a piston 28reciprocable in a relatively fixed cylinder 30 and carrying camfollowers as particularly illustrated andV described in `United-Statesapplication Serial No. 184,792, re-

-ferred to above. Hydraulic fluid is led to a passage 32 in the shaftIII from a suitable conduit 34 and .oil transfer bearing 36 andhydraulic fluid from a different source is also led to a conduit 38within the propeller shaft through a tubular connection40. Both of thepassages 32 and 40 lead Fig. 4 is a detailed sectional view on anenlarged to a valve generally indicated at 42 which, when subjected topressures below a predetermined limit, connects the passage 32 with theinterior of the cylinder 30 at the pitch increasing side of the piston28 and connects the passage 38 with the interior of the cylinder 30 atthe pitch decreasing side of the piston. This position of the valve 42is shown in Fig. 1. When subjected to pressures above the abovementioned predetermined llmits the connection of these passages to therespective ends of the cylinders is reversed. The passage 32'is thenconnected to the interior of the cylinder at the pitch reducing side ofthe piston 28 while the passage 38 is connected to the interior of thecylinder at the pitch increasing side of the piston. Within the shaft I0the passages 32 and 38 are separated and the end of the passage 32 isclosed by a suitable plug 44 disposed in the bore of the shaft,Referring now to Fig. 2 it will be observed that the conduit 34 leads tothe outlet side of a governor, generally indicated at 48 and the passage38 is connected by the conduit 4U with a pump 48 which may be the engineoil supply pump the outlet pressure of which is controlled by thepressure relief valve 50. From the pump outlet conduit 40 a passage 52leads to the engine lubricating system and a passage 54 leads to thegovernor 46. This governor may include a booster pump and a governoractuated valve disposed between the outlet of the booster pump and thepassage 34 which construction is particularly illustrated and describedin United States Patent No. 2,204,640, issued June 18; 1940, to Elmer E.Woodward for Governor mechanism.

With the arrangement so far described it is apparent that Voil at enginelubricating oil pressure will be continuously supplied to the interiorof the cylinder 30 at the pitch decreasing side ci the piston 28 whileoil from the governor, at a pressure controlled by` the governor boosterpump, will be supplied to the cylinder 30 at the pitch increasing sideof the piston 28 under the control of the governor actuated valve whichacts to connect the space at the pitch increasing side of the pistonwith the outlet of the booster pump or with a drain, presently to bedescribed, as the governor demand for a change of speed may require. Asis clearly set forth in my co-pending United States application SerialNo. 184,792, referred to above, the pitch changing mechanism is providedwith some form of intermediate pitch limit stop which will prevent themechanism from turning the blades beyond a predetermined high pitchposition when actuated by hydraulic fluid at the pressure supplied bysaid governor booster pump to keep the pitch within the range ofconstant speed control.

When it is desired to bring the propeller to a feathered position highpressure fluid from any suitable source is supplied to channel B andpreferably electrically controlled. In the structure chosen fordisclosing the invention a motor 56 is energized to drive a highpressure pump 58 the outlet of which is connected through a channel E0with a valve 62 which acts, when subjected to high pressure fluid fromthe pump 58 to block olf the governor outlet channel 64 and connect thechannel 34 directly with the outlet of the pump 58 to supply hydraulicfluid at the increased pressure, sufficient to override the intermediatepitch limit stop mentioned above, to the space within the cylinder 30 atthe pitch increasing side of the piston 28 to rotate the propellerblades to their limiting high pitch or feathered position.

Energization of the motor 56 is controlled by a relay switch 66interposed in the circuit between the motor and the source of power suchas the battery 68. This relay switch is urged toward its open positionby a spring 'l0 and is closed by a solenoid 12 the energization of whichis controlled by a manually operable switch 14. Switch 14 is urgedtoward its open position by a spring 16 and retained in closed positionby a solenoid 18 the energizing circuit of which includes the pressureoperatedrswitch 80 hydraulically connected with the channel 60 in such amanner that fluid pressure in the channel 60 at a predetermined valuewill open this switch. Opening of switch 80 de-energizes the solenoid 18and permits switch 14 to open under the influence of the spring 16 thusde-energizing the solenoid 12 and permitting the relay switch 66 to openunder the influence of the spring 10. Opening of switch 86 de-energizesthe motor B and stops the pump 58. The predetermined pressure valueselected is a value slightly above the maximum required to turn thepropeller blades in a pitch increasing direction between intermediatehigh pitch position and feathering position indicating that thepropeller has reached its full feathered condition.

Since the pressure necessary to feather the propeller is not always thesame, varying somowhat with the viscosity of the hydraulic fluid and theresistance met'by the fluid exhausted from the space at the pitchdecreasing side of the piston it has been found desirable to connect thespace at the side of the switch actuating member opposite the space atthe side connected with the channel 60 to the channel 40 through whichthe fluid vents from the pitch decreasing end oi the cylinder 30. Such afluid connection is indicated at 8l. This arrangement causes thepressure actuated cut-out switch to operate on the difierence betweenthe pressure of the fluid supplied to the pitch increasing side of thepitch changing mechanism and the pressure of the fluid vented from thepitch decreasing side of the mechanism when the propeller is brought toits feathered position which arrangement gives a more sensitive actionof the switch and insures that the propeller will have reached a fullyfeathered condition before the feathering circuit is broken by theswitch 80.

It has been assumed that the switch shown in Fig. 2 is of the same formas the switch shown in Fig. 3 which has been generally designated byl,the numeral 80 while the somewhat modified form of switch shown inFig. 4 is generally designated by the numeral 80.

The switch B0 comprises a casing 82 which may be conveniently formed asa metal casting or forging. This casing has a flat plate 84 forcooperation with the flat face of a pad 86 to which the switch isattached, a gasket 88 being preferably included between the switch andthe pad to prevent leakage of fluid through this joint. The pad B6 isformed integrally with some portion of the control apparatus, forexample with the base or pad 90 of the governor 40 and the switch issecured to the pad by suitable means such as the screws 92. Within thecasing B2 there is a cylindrical bore 94 having a reduced cylindricalextension 96 at one end thereof the end of which is closed by the wallof the casing and having an internally screw threaded portion 58 at theopposite open end thereof. An insulating bushing |00 is molded onto aplunger' |02 and positioned in the reduced extension 96 of thecylindrical bore. The plunger |02 carries a contact portion |04 andextends through this bushing to a position near the closed end of theextension 96. A second contact member |06 is secured in the closed endof the extension 94 in position to cooperate with the contact member |04and is connected with a return to the battery B8 which may be throughthe ground indicated at |08. At its end opposite the contact member |04the plunger |02 projects into the chamber ||0 formed by the innerportion of the bore 94 and carries an abutment ||2 for one end of acompression spring ||4 the opposite end of which bears against anabutment ||6 formed on the inner end of a connector ||8 fixed in aterminal member |20 by a bushing |22 of insulating material. Theterminal member |20 is provided with an externally threaded portionwhich cooperates with the threaded portion 98 of the bore 94 and with ashoulder |24 which provides a nut for turning the member |20 and alsocooperates with the gasket |26 to provide a seal between the member |20and the casing 82. It is to be understood, however, that the terminalmember may be secured to the casing by other suitable `membr-irs |84 and|05.

means such, for example. as flange bolts or a gland nut. The channel lvleads into thechamber iii! and the channel t is led to the space at theclosed end of the cylindrical extension 96 ol the bore 94 which spacecontains the contact The bushing .|00 is preierably `formed ofinsulating material. such as a thermo-setting phenolic condensate and isdimensioned to provide a positive clearance between itself and the wallof the/bore 96 so that a small quantity of the i'iuidiorced underpressure into the space between the inner end of this bushing and theclosed end of the bore will pass into the chamber ||0 denned by thelarger bore S4, and into the drain channel 8| to prevent accumulation ofsludge and congealing of o-l in the contact chamber` The spring ||4 issufficiently resilient to permit separation of the contact members .|04and |05 when the pressure of the iluid in the Space at the closed end ofthe bore reaches the selected value at which the circuit through thepressure switch is to be broken. When the pressure of the uid in thespace containing the contact members |04 and |06 reaches the valueindicated these `embers will be separated breaking the circuit andde-energizing the ieathcring pump motor.

While the electrical-contact between the members |02 and ||8 is shown tocomprise the spring H4 it is to be understood that an additionalflexible electrical conduit can be secured between these two members ifdesired,

In the slightly modied form of the invention shown in Fig. 4, the casing|28 is substantially the same as the casing 82 of the switch shown inFig. 3 and has an internal bore |30 with a cylindrical extension |32 atone end thereof the end of the extension being closed bythe end wall ofthe casing. At the open end of the bore casing is provided with acylindrical extension i. |34 having external screw threads for therecep-v tion of the internal screw threadsin the end of a terminalmember |36. This terminal member is provided with an internal shoulder|38 which engages the edge of a circumferential flange provided on asealing member` |40 which carries the connecting plug H8. The bodyportion of the sealing member |40 is dispo-sed within the cylindricalportion |34 of the casing |28 to pro-y vide a hrm support for the memberin the casing. Witl'i this arrangement seal member |40 can beindependently removed from the casing when the terminal member |36 hasbeen removed. The

- factoring standpoint.

extension |32 contains a resilient bushing |42 of v some suitablematerial .such as rubber or syn-` thetic rubber and through this bushingextends a stem M4 similar to the stem |02 and carrying a contact member|46 which cooperates with a contact member |48 secured in the end wallof the casing. A spring |50 extends between suitable abutments carriedrespectively by the members H8 and- |44 and, if desired, a liexibleelectrical conduit may be connected between these members. A channel |52leads to the space containing the contact members |46 and'MB and achannel |54 leads into the chamber containing the spring |50, thechannel |52 being arranged lor connection with the high pressure channel|50 in the governor base and the channel |54 being arranged forconnection with the lowV pressure channel 8| in the governor base in themanner described above.

The switches shown in Figs. 3 and 4 both operate in the same manner, thestructural dierences shown in these two embodiments of the inventionbeing mainly important from a manu- In the switch mechanism shown inFig. 3 the sealing member |22 is molded into the terminal member |20around the internal shoulder |56 `and the connecting plug ||8 whichmeans thatthe terminal member and the connecting plug both have to be athand when the molding or vulcanizing process is performed and that thethree members namely the terminal |20, the bushing |22 and theconnecting plug I8 constitute a single unit when the bushing has been vformed in place. In the form shown in Fig. 4 the seal member or bushing|40 can be made separately and thereafter the connecting plug ||8 can beinserted through an aperture in the bushing and riveted in place and theunit comprising the bushing |40 and connecting plug ||8 can be assembledwith the switch when the terminal |36 is screwed into place on thecylindrical extension of the casing, In this case the terminal |36 andconnecting plug ||8 do not have to be incorporated in the structureduring the molding or vulcanizing process and these various units can bebrought together and assembled by the manufacturer or user of theswitch.

While two slightly different mechanical arrangements have beenhereinabove described and illustrated in the accompanying drawing it isto be understood that various other structural modiiications may beresorted to without in any way changing the method of operation of theswitch or exceeding the scope of the invention so long as the structureprovides that the make and break contact members are immersed inhydraulic fluid at thc time they become operative to interrupt thecircuit including this switch. While it is desirable that the switchoperate on the difference between the high pressure and the low pressuresides of the hydraulic mechanism, it is within the scope of theinvention that the switch should operate only on the pressure of thehigh pressure side.

While a suitable mechanical embodiment in two somewhat different formshas been hereinabove describcdand illustrated in the accompanyingdrawing for the purpose of disclosing the invention, it is to beunderstood that the invention is not'limited to the particularembodiment so described and illustrated, but thatV- such, changcsin thesize, shape and arrangement of the various parts and of the materials ofwhich they are formed `may be resorted to as come within the scope ofthe sub-joined claims.

Having now described the invention so that others skilled in the art mayclearly understand the same, what it is desired to secure by LettersPatent is as follows:

1. A switch Vcomprising a casing, a contact member fixed therein, asleeve of insulating material within said casing, and a, movable Contactmember supported thereby for movement toward and from said xed contactmember, means resiliently urging said movable contact member intocontact with said xed Contact member, said casing having two pressurechambers therein separated by said sleeve and passages for introducinguid under pressure simultaneously into said chambers, whereby variationsof fluid pressure within said chambers will open said switch and permitsaid switch to close.

i, 2. A switch comprising a casing having a chamber therein and acounterbore of smaller diameter than said chamber extending from saidchamber to adjacent one end of said casing, a fixed contact memberextending through said casing into the closed end of said counterbore, abushing of insulating material separating the closed end of saidcounterbore from'said chamber, a movable contact member mounted in saidbushing and extending into said counterbore, resilient electricalconducting means urging said movable contact member into contact withsaid fixed contact member and forming a part of the circuit controlledby said switch, and a passage in said casing opening into saidcounterbore at the closed end thereof to admit fluid under pressure tosaid counterbore at the side of said bushing opposite said resilientmeans to open said contact.

3. In a fiuid pressure actuated cut-out switch, a hollow casing, movablemeans comprising an electrical contact member and an insulating bushingtherefor dividing the interior of said casing into two separatechambers, respective fluid channels leading to said chambers, and afixed contact member in one of said chambers in electrical contact withsaid casing and cooperating with said movable contact member to make andbreak an electrical circuit including said switch, an electricalconnector insulatedly carried at one end of said chamber, and a springurging said contact'l members together and constituting the soleelectrical connection between said connector and said movable contact.

4. The arrangement as set forth in claim 3 in which said bushing isdimensioned to provide clearance between itself and said casing toprovide a restricted passage for the ow of fiuid from one of saidchambers to the other chamber.

5. A fluid pressure actuated electric switch comprising, a unitarycasing adapted to be mounted on a machine surface and having at one sidethereof a fiat external surf ace and interiorally thereof a bore open atone end and closed at the opposite end and providing tandem pressurechambers, and fluid passages extending one from each pressure chamberand opening to said flat surface, a, fixed contact member mounted insaid casing at the closed end of said bore, an insulating bushingslidable in said bore between said fluid passages, and a movable contactmember carried by and extending through said bushing.

6. A fluid pressure actuated electric switch comprising, a unitarycasing adapted to be mounted on a machine surface and having at one sidethereof a flat external surface and interiorly thereof a bore open atone end and closed at the opposite end and providing tandem pressurechambers, and fluid passages extending one from each pressure chamberand opening to said flat surface, a fixed contact member mounted in saidcasing at the closed end of said bore, an insulating bushing slidable'in said bore between said fiuid passages, and a movable contact membercarried by and extending through said bushlng, said contact membersconstituting 'a stop for said busihng to restrain said bushing fromcovering the end of one of said fluid passages.

'1. In a fluid pressure actuated switch, a unitary casing comprising aflat plate base portion having a fiat surface, and a cylindrical portionextending across said base portion and provided with an internal borethe axis of which is substantially parallel to said fiat surface andwhich is closed at one end by the casing wall, a fixed contact membersecured in said casing, a plunger in said bore separating said bore intotwo fluidV chambers each connected through a respective fluid channelwith the face surface of said base portion, and a movable contact membercarried by said plunger.

8. In a uid pressure actuated switch, a unitary casing comprising -abase portion having a fiat face surface, and a chamber portion having abore the axis of which is substantially parallel to said face surfaceand which is closed at one end by a wall of said-casing, a fixed contactmember carried by said casing at one end of said bore, means including amovable contact member dividing said bore into separate pressurechambers each connected through a respective fiuid channel with saidflat face surface, and a current conducting spring in said boreresiliently urging said movable contact member toward said fixed'contactmember.

9. In an oil pressure actuated switch, a casing having a high pressurechamber and a low pressure chamber and an intercommunicating cylinderwall therebetween, a fixed contact in said high pressure chamber, aninsulated piston slidable in said cylinder wall and carrying a movablecontact, and a spring in said low pressure chamber electricallyconnected to said movable contact and urging the same into engagementwith said fixed contact, said piston being smaller than said cylinderwall and having a clearance to permit passage of oil from said highpressure chamber around and past said piston to said low pressurechamber.

10. In an oil pressure actuated switch, a casing having a high pressurechamber and a low pressure chamber and an intercommunicating cylinderwall therebetween, a fixed contact in said high pressure chamber, aninsulated piston slidable in said cylinder wall and carrying a movablecontact, and a spring in said low pressure chamber urging said pistontoward said fixed contact to maintain said movable contact in engagementtherewith, said casing having a passage connected with an actuatingsystem and said high pressure chamber for admitting high pressure oilfrom the actuating system to said high pressure chamber and anotherpassage connected with said actuating system and said low pressurechamber Vfor returning oil from said low pressure chamber to theactuating system, and said piston being smaller than said cylinder walland having a clearance for the passage of oil from said high pressurechamber to said low pressure chamber.

11. In an oil pressure actuated switch, a casing having a high pressurechamber and a low pressure chamber, a fixed contact in said highpressure chamber, an insulated piston subject to said high pressure andcarrying a movable contact, a spring in said low pressure chamberelectrically connected to said movable contact and urging the same intoengagement with said fixed contact, said low pressure chamber having aninsulated wall, and a terminal carried by said wall forming a seat and aguide for said spring and forming a stop for said movable contact.

12. In an oil pressure actuated switch, a metal casing having a rst boreand a smaller bore extending therebeyond, a fixed contact grounded insaid smaller bore, an insulated piston slidable in said smaller bore andcarrying a movable contact having a head extending into said first bore,an insulated plug closing said first bore and supporting a terminal stemhaving a head extending into said first bore, and a. coiled compressionmetal spring surrounding said terminal head and seated thereon andbearing against the head of said movable contact.

13. A switch forming a portion of a liquid system and comprising acasing having a pressure chamber therein, a fixed contact memberextending into said chamber, a second chamber in said casing, a slidablebushing of insulating material separating said chambers and having a.contact member mounted therein and extending into the chamber containingsaid xed contact, said bushing having clearance in said casing toprovide a restricted connection between said chambers, means to admitliquid under pressure from said liquid system to said chamber containingsaid fixed contact to open said contacts, and means for conductingliquid from said second chamber to said liquid system, some of saidliquid under pressure moving through said restricted connection from thecontact chamber to said second chamber to prevent an accumulation ofsludge and congealing of liquid in said contact chamber.

ERLE MARTIN.

THOMAS E. DOHERTY.

